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California Groundwater Reliance Linked To Increased Earthquake Activity

May 15, 2014
Image Caption: Satellite view of San Andreas Fault and surrounding region in California. Credit: Thinkstock.com

redOrbit Staff & Wire Reports – Your Universe Online

Increased use of groundwater or pumping and irrigation could be increasing the number of small earthquakes occurring in California, and eventually speed-up the frequency of larger ones, according to new research appearing in the journal Nature.

According to BBC News environmental correspondent Matt McGrath, the study found that extracting water for human activities has been causing mountains to lift and valleys to subside, increasing seismic activity across the state’s main fault – the San Andreas Fault, which runs north-south through western California and is part of the boundary between the Pacific and North American tectonic plates.

The San Andreas Fault was responsible for the 1906 San Francisco earthquake and several other seismic events over the years, and part of the concern is that the fault is overdue for a large quake (magnitude 6.7 or greater), explained Sarah Zielinski of Smithsonian.com. That large of an earthquake could cause severe destruction in some of the state’s largest cities, including Los Angeles, she added.

Lead author Dr. Colin B. Amos, of Western Washington University, and his colleagues analyzed data from GPS systems throughout California and Nevada in order to analyze the lifts and dips in the San Joaquin valley’s topography. The valley is one of the most productive farm regions in the US, but that success is heavily reliant upon access to ground water for crop irrigation, reported McGrath.

“So great is the demand that scientists estimate twice as much water is being consumed as is being returned through rain and snow,” he added. “All this extraction is having a significant impact on the shape of the Earth. The floors of the valleys are subsiding, the researchers found, while the surrounding mountains are on the rise.”

“We are removing a weight from the Earth’s crust and it is responding by flexing upwards and literally moving mountains,” Dr. Amos told BBC News. “It seems as though these small stress changes that happen on a yearly basis, are causing more small earthquakes to occur on portions of the fault.”

Based on their measurements, the study authors reported that the area surrounding the San Joaquin Valley is rising by between one to three millimeters each year in order to compensate for subsidence in the valley itself, said Zielinski. That subsidence is believed to be the result of water being removed from the aquifer beneath it, as roughly 42 trillion gallons (160 cubic kilometers) of water have been removed from it over the past 150 years.

While the uplift in the region does not appear to be much, it is substantial enough to “increase the sliding on the San Andreas fault system” by altering the loads burdening the fault, Paul Lundgren, of the California Institute of Technology, wrote in an editorial accompanying the study, according to Smithonian.com.

“Over the long-term (a 100-year timescale), the unloading generated by constant water extraction… enhances the accumulation of stress between the occurrence of large earthquakes, bringing faults such as the San Andreas closer to failure,” he continued. The study authors added that human activities “may give rise to a gradual increase in the rate of earthquake occurrence, as suggested by earthquake catalogues in central California.”

Unfortunately, Zielinski said, the state’s reliance on groundwater shows no signs of lessening. California’s population is increasing, the state is stuck in a severe drought, and the annual snowpack for 2014 was far smaller than normal. Those factors will lead to increased groundwater demand for agricultural and other uses. Based on this new research, however, it appears as though there will likely be consequences for that groundwater reliance.


Source: redOrbit Staff & Wire Reports - Your Universe Online



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